RennTech Performance Ecu Upgrade For Mercedes-Benz X166 GLS 550 Biturbo

VENDOR: RennTech

SKU: 54.166.GLS550BI

All orders will include an AutoTalent window decal


RennTech HHT (hand held tuner) allows you the unlimited ability to switch between tuned and stock ECU programming and requires no ECU removal. RennTech proprietary tuning module stores both the RennTech tuned file and your vehicles stock file. The module plugs directly into the OBD2 port and delivers the file you choose directly to the ECU. Programming takes only a few minutes and the vehicle can be reflashed at any time as many times as you wish.

RennTech intermediate level ECU upgrade for the Mercedes M278 engine still offers huge gains in performance across the entire RPM range, but with a slightly reduced peak HP and torque from our standard tune. This is ideal for customers who want increased performance in their daily driver without worry of extra strain on driveline components or for areas and countries with extreme altitudes, temperatures or fuel quality concerns.

RennTech intermediate ECU tune increases performance from 449 HP and 538 lb/ft torque up to 500 HP and 605 lb/ft at the crank! This is a slight reduction from our standard tune but still offers white knuckle performance at one of the most affordable price points in the tuning market.


We have found the M278 engine stock performance numbers vary from the baseline figures claimed by Mercedes Benz. We typically see higher baseline numbers than claimed by the factory.

Power gains are calculated based on stock numbers measured by RENNtech.

Crank Performance Numbers are calculated with a 18% Drivetrain loss on 4MATIC SUVs.

Our numbers will be dependent on conditions and fuel quality. 91+ Octane gasoline is mandatory with this Performance Upgrade.

States known for poor fuel quality have to be supplied with a lower power setup


  • Provides ability to switch between tuned and stock ECU programming
  • Providing comfort or daily driver reliability
  • Significant gains in horsepower
  • Increases the performance
  • Significant gains torque 
  • Gains: +26HP / +67LB-FT

Stock Performance:

  • 449 HP @ 5,500rpm; 516 LB-FT @ 2,000-4,500rpm
  • 474 HP @ 5,500rpm; 538 LB-FT @2,800-3,900rpm

Modified Performance:

  • 500 HP @ 5,500rpm; 605 LB-FT @ 3,700rpm
  • 410awhp @ 5,500rpm; 496awtq @ 3,700rpm

Vehicle Fitment:    

  • 2016 Mercedes-Benz X166 GLS 550 Biturbo
  • 2017 Mercedes-Benz X166 GLS 550 Biturbo
  • 2018 Mercedes-Benz X166 GLS 550 Biturbo
  • 2019 Mercedes-Benz X166 GLS 550 Biturbo
  • 2020 Mercedes-Benz X166 GLS 550 Biturbo


                            Images are for representation purpose only and may differ depending on application.